This invention provides for improved means to produce binding specific proteins using concatamers of semi-randomly generated oligonucleotides inserted into genes encoding the external domains of bacterial outer membrane proteins. The genes are induced to express and the bacteria are then screened for the ability to bind to predetermined compositions. Those clones carrying the desired binding protein are isolated, cultured and the protein purified. Increased avidity of the binding specific proteins are achieved by reisolating the oligonucleotides which conferred binding affinity and mixing them with new semi-randomly generated oligonucleotides to generate a population enriched for oligonucleotides that had previously conferred to bacteria the desired binding affinity. The enriched population of oligonucleotides is then religated to the gene encoding the external domain of the bacterial protein, the gene is inserted into a bacterial cell and the cells analyzed for increased avidity for the predetermined composition.
Semi-random oligonucleotides have been previously identified as a means to obtain binding proteins specific for a predetermined composition. Typically such work involves recombinantly inserting short oligonucleotides into the binding sites of antibodies and laborious screening procedures. CA patent application Ser. No. 2,035,384. Other work involves assaying a phage library having random inserts. WO 91/050058 describes a cell-free method for screening random peptides for binding specificity.